Defined in header <stddef.h>
typedef /*implementation-defined*/ max_align_t;
max_align_t is a type whose alignment requirement is at least as strict (as large) as that of every scalar type.
max_align_t is usually synonymous with the largest scalar type, which is long double on most platforms, and its alignment requirement is either 8 or 16.
 See also
C++ documentation for max_align_t